Systems for assessing and cutting bioprosthetic tissue

ABSTRACT

Systems, dies, and methods are provided for processing pericardial tissue. The method includes positioning a die-cut assembly over the pericardial tissue, the die-cut assembly including a die having a plate, a die pattern, and an opening, the die pattern attached to the plate, the opening formed in the plate to provide access to the pericardial tissue, and measuring a thickness of the tissue through the opening. The die-cut assembly may be mounted for automated vertical movement, and a platen on which the tissue is placed is capable of automated horizontal movement. Different target areas on the tissue can be assessed by measuring the thickness through the die, and when an area is deemed suitable the die pattern cuts a shape therefrom. The system is useful for cutting uniform thickness heart valve leaflets, and can be automated to speed up the process.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/459,543, filed Jul. 1, 2019, now U.S. Pat. No. 11,076,953, which is acontinuation of U.S. patent application Ser. No. 15/173,435, filed Jun.3, 2016, now U.S. Pat. No. 10,335,271, which is a divisional of U.S.patent application Ser. No. 13/538,684, filed Jun. 29, 2012, now U.S.Pat. No. 9,358,107, which claims the benefit of U.S. Patent ApplicationNo. 61/503,471, filed Jun. 30, 2011, the entire contents all of whichare incorporated herein by reference for all purposes.

FIELD OF THE INVENTION

The inventive subject matter generally relates to processing pericardialtissue, and more particularly relates to systems and methods forassessing and cutting pericardial tissue for the manufacture ofprosthetic heart valves.

BACKGROUND OF THE INVENTION

A heart of a mammalian animal is a hollow muscular organ having left andright atria and left and right ventricles, each provided with its ownone-way valve. A natural heart includes aortic, mitral (or bicuspid),tricuspid and pulmonary valves, and each valve has one-way leaflets tocontrol a directional flow of blood through the heart. The valves areeach supported by an annulus that comprises a dense fibrous ringattached either directly or indirectly to the atrial or ventricularmuscle fibers. Over time, the heart (, the valve) may become diseased ordamaged. To repair the heart, the valve may undergo a valve replacementoperation. In one operation, the damaged leaflets of the valve areexcised, and the annulus is sculpted to receive a replacement valve,such as a prosthetic heart valve. Although various types andconfigurations of prosthetic heart valves for replacing diseased naturalhuman heart valves are known, such valves conventionally comprise avalve and a sewing ring supporting valve leaflets and commissure posts.

Bio-prosthetic valves can be formed from an intact, multi-leafletporcine (pig) heart valve, or by shaping a plurality of individualleaflets out of bovine (cow) pericardial tissue and combining theleaflets to form the valve. The pericardium is a sac around the heart ofvertebrate animals, and bovine pericardium is commonly used to makeindividual leaflets for prosthetic heart valves.

Steps in a typical commercial process for preparing pericardial tissuefor heart valve leaflets include first obtaining a fresh pericardialsac, and then cutting the sac open along predetermined anatomicallandmarks. The sac is then flattened and typically cleaned of excess fatand other impurities. After trimming obviously unusable areas, a windowor patch of tissue is fixed, typically by immersing in an aldehyde tocross-link the tissue. Rough edges of the tissue window are removed andthe tissue bio-sorted to result in a tissue section. The process ofbio-sorting involves visually inspecting the window for unusable areas,and trimming the section therefrom.

The section is then placed flat on a platform for thickness measurementusing a contact indicator. The thickness is measured by moving thesection around the platform while a spindle of the indicator movesup-and-down at various points. The thickness at each point is displayedand recorded. After sorting the measured sections by thickness, leafletsare die cut from the sections, with thinner leaflets generally beingused for smaller valves, and thicker leaflets being used for largervalves. Of course, this process is relatively time-consuming and thequality of the final leaflets is dependent at several steps on the skillof the technician. Moreover, the number of leaflets obtained from eachsac is inconsistent, and subject to some inefficiency from the manualselection process.

To help speed up the process of identifying areas of similar thicknessin the pericardial sections, a system and method to topographically mapthe sheet into similar thickness zones for later use is disclosed inU.S. Pat. No. 6,378,221 to Ekholm, Jr., et al. The system includes athree-axis programmable controller for manipulating a bio-materialworkpiece with respect to a thickness measurement head which has aplurality of thickness gauges or sensors for simultaneous measurement ofa plurality of points, with the sensors being adapted to contact thesheet or not. A marking head may be provided for marking the zones orotherwise indicating the thickness in different areas. The measured ormarked sheet is then removed from the system for further processing intoleaflets.

Despite advancements in assessing bioprosthetic tissue for heart valveleaflets and other uses, there remains a need for a more accurate andefficient process. Additionally, the need is more important for thinnerleaflets, such as used in smaller surgical valves or incompressible/expandable valves for percutaneous or minimally-invasivesurgeries, since the presence of uneven or mismatched leaflets isrelatively more detrimental to proper valve functioning.

SUMMARY OF THE INVENTION

In an embodiment, by way of example only, a method of processingpericardial tissue is provided. The method includes positioning adie-cut assembly over the pericardial tissue, the die-cut assemblyincluding a die having a plate, a die pattern, and an opening, the diepattern attached to the plate, the opening formed in the plate toprovide access to the pericardial tissue, measuring a thickness of thetissue through the opening, selecting a section of the pericardialtissue based on the thickness measurement, and cutting the pericardialtissue with the die. The die-cut assembly may be mounted for automatedvertical movement, and a platen on which the tissue is placed is capableof automated horizontal movement. Different target areas on the tissuecan be assessed by measuring the thickness through the die, and when anarea is deemed suitable the die pattern cuts a shape therefrom. Thesystem is useful for cutting uniform thickness heart valve leaflets, andcan be automated to speed up the process.

In another embodiment, by way of example only, a die is provided forforming a leaflet of a prosthetic valve. The die includes a plate, a diepattern attached to the plate and having a shape resembling the leafletand defining a boundary, and an opening formed through the plate withinthe boundary of the die.

In still another embodiment, by way of example only, a system forprocessing pericardial tissue is provided. The system includes a die anda shield. The die has a plate, a die pattern, a cutting edge, and anopening. The die pattern is attached to the plate and has a shapedefining a boundary. The opening is formed through the plate within theboundary of the die pattern. The shield is configured to be disposedbetween the die and the pericardial tissue to prevent contact betweenthe cutting edge of the die and the tissue, and the shield has a windowconfigured to receive the die pattern.

A further understanding of the nature and advantages of the presentinvention are set forth in the following description and claims,particularly when considered in conjunction with the accompanyingdrawings in which like parts bear like reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a system for assessing and cuttingpericardial tissues, according to an embodiment;

FIG. 2 is a top view of a die assembly for use with the system of FIG. 1, according to an embodiment;

FIG. 3 is a bottom, perspective view of the die assembly of FIG. 2 ,according to an embodiment;

FIG. 4 is a perspective view of a shield for use system of FIG. 2 ,according to an embodiment;

FIG. 5 is a flow diagram of a method of processing pericardial tissue;

FIG. 6 is a plan view of an exemplary heart valve leaflet cut with a diein accordance with the principles described herein;

FIGS. 7 and 8 are magnified sectional views through exemplarybioprosthetic tissue illustrating typical physical compositions;

FIGS. 9A-9D illustrate a semi-automated system for assessing and cuttingheart valve leaflets from pericardial tissue.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description is merely exemplary in nature and isnot intended to limit the inventive subject matter or the applicationand uses of the inventive subject matter. Furthermore, there is nointention to be bound by any theory presented in the precedingbackground or the following detailed description.

Typically, methods of preparing pericardial tissue for use in theformation of bio-prosthetic valve leaflets involve cutting out patchesfrom the tissue and measuring the thickness or other physicalcharacteristics of the tissue patch, sorting the tissue patches based onthese physical characteristics, cutting the tissue into the shape of aleaflet, and then sending the tissue on for further processing. Eachstep of the process is performed separately.

Improved systems and methods for processing pericardial tissue intoheart valve leaflets are provided. Generally, the systems include athickness gauge, a die and a shield. The die has a plate, a die pattern,a sharp cutting edge, and an opening. The die pattern is attached to theplate and has a shape defining a boundary. The opening is formed throughthe plate within the boundary of the die pattern. The shield isconfigured to be disposed between the die and the pericardial tissue toprevent inadvertent damage to the tissue from the sharp cutting edge ofthe die and has a window configured to receive the die pattern. Thesystems and methods can be used in the manufacture of valve leaflets orother components of a bio-prosthetic heart valve. For example, otherprosthetic valve components typically having thickness specificationsmay benefit from the improved systems and methods as well. These systemsand methods allow for the optimization of the valve leaflet formationprocess.

FIG. 1 is a perspective view of a system 100 for processing pericardialtissue 102, according to an embodiment. The system 100 includes athickness gauge 104 and a die-cut assembly 106. The thickness gauge 104is configured to measure a thickness of the tissue 102 and includes astand 108 and a detection component 110. The stand 108 has a platform112 that is sized and shaped to provide a surface on which the tissue102 can be positioned. In an embodiment, the platform 112 is generallyrectangular. In other embodiments, the platform 112 is round, oval orhas another configuration. The stand 108 can also include a mounting rod114 that is coupled to the platform 112. For example, the mounting rod114 extends generally perpendicular from the platform.

The detection component 110 is mounted to the rod 114 via a coupling arm115. In an embodiment, the coupling arm 115 has an end through which themounting rod 114 is inserted and a tightening mechanism for temporaryattachment to the rod 114. In this way, the coupling arm 115 can beadjusted between various positions along a length of the mounting rod114. The detection component 110 has a readout component 118 that isattached to an opposite end of the coupling arm 115 and is positionedover the tissue 102. In an embodiment, a measurement probe 120 extendsdirectly from the readout component 118 for placement over the tissue102 to measure the thickness of the tissue.

In other embodiments, the thickness gauge 104 may be a standalone devicethat does not include stand 108. In such case, the readout component ofthe thickness gauge can be placed in the vicinity of the tissue 102, andthe measurement probe of the readout component, which can extend from awire or can be wirelessly coupled to the readout component, can bemanually positioned over the tissue 102.

The die-cut assembly 106 is placed over the tissue 102 and includes adie 122 and a shield 124. Generally, the shield 124 is used to preventthe sharp, cutting edge of the die from inadvertently contacting thetissue and damaging it. The shield 124 is positioned over a selectedspot on the tissue 102, and the die 122 is disposed on the shield 124.The die-cut assembly 106 can be moved from spot to spot on the tissue102 without damaging the tissue so that areas with undesired thicknessesor blemishes on the tissue 102 can be avoided.

FIG. 2 is a top view of the die 122 of FIG. 1 , and FIG. 3 is a bottom,perspective view of the die assembly of FIG. 2 , according to anembodiment. The die 122 is used for identifying a suitable area on thetissue 102 to cut and for then cutting a desired design from theidentified area. The die 122 includes a plate 125, a die pattern 126,and an opening 128, in an embodiment. The plate 125 provides an area forgrasping and can be generally rectangular, in an embodiment. In otherembodiments, the plate is round, oval or another shape. The plate 125includes a first major surface 130, an opposite second major surface132, and side surfaces 134 extending between the first and second majorsurfaces 130, 132. To provide sufficient structural integrity, the plate125 preferably comprises a thermoplastic material including one of anacrylic glass and polycarbonate (PC) material or anothershatter-resistant material.

The die pattern 126 is attached to and extends from the first majorsurface 130. In an example, the die pattern 126 includes a portion 127that is embedded within the plate 125 and an exposed portion 129 thatextends from the plate 125. The exposed portion 129 of the die pattern126 has a height that is greater than a thickness of the tissue 102. Toensure that the die pattern 126 can pierce through the tissue, the diepattern 126 has a sharpened cutting edge 136 and preferably comprises ametal material. Suitable materials include, but are not limited to,stainless steel and the like.

The die pattern 126 forms a generally closed shape defining a boundary.In an embodiment, the die pattern 126 has a leaflet shape for formingone leaflet used in the manufacture of the bio-prosthetic heart valve. Abio-prosthetic heart valve leaflet typically includes a straight free orcoapting edge having opposed tab ends, and a generally semicircular cusptherebetween and opposite the coapting edge. Thus, as illustrated, anexemplary die pattern 126 for cutting a valve leaflet has a curvedportion 138 and a straight portion 140 with tab ends 143. In anembodiment, the curved portion 138 is a semicircle. In still anotherembodiment, the curved portion 138 forms an arc with multiple radii. Inan embodiment, the straight portion 140 encloses the curved portion 138and extends from one end of the curved portion 138 to another.Alternatively, the straight portion 140 includes tabs 143 that extendfrom the straight portion 140 and couple the straight portion 140 to thecurved portion 138. In accordance with another embodiment, the diepattern 126 has a shape for forming another component of the prostheticheart valve.

The opening 128 is formed through the plate 125 and extends between thefirst and second major surfaces 130, 132. To insure that the portion ofthe tissue 102 being measured will have a suitable thickness forformation of the prosthetic valve, the opening 128 is disposed withinthe boundary of the die pattern 126. In an embodiment, a single opening128 is formed in the plate 125. In an embodiment, the location of theopenings may be adjacent to the straight portion 140 of the die pattern126. The opening 128 can be rectangular and is dimensioned toaccommodate the measurement probe 120 (FIG. 1 ) of the thickness gauge104. In another embodiment, the dimensions of the opening 128 are suchthat at least three thickness measurements can be taken at differentspots on the tissue 102.

In another embodiment, more than one opening is included. For example,three openings 141 (shown in phantom in FIG. 2 ) can be formed inselected locations in the boundary of the die pattern 126. Thus,thickness measurements can be taken in the same place each time andtherefore be consistent for each valve component formed using the die122. The openings 141 are configured to receive the measurement probe120 (FIG. 1 ) of the thickness gauge 104. Although the openings 141 areshown as being generally circular, they can have any alternate shapethat can accommodate the measurement probe 120.

Turning now to FIG. 4 , a perspective view of the shield 124 for usewith the system 100 of FIG. 2 is provided, according to an embodiment.The shield 124 preferably comprises a metal material, and in someembodiments, the shield 124 can comprise stainless steel and the like.The shield 124 has a base 142 and a handle 144, in an embodiment. Thebase 142 has a window 146 that is configured to allow the exposedportion 129 (FIG. 3 ) of the die pattern 126 to extend. In anembodiment, the base 142 includes two bifurcated prongs 148, 150 thatare spaced apart to define a portion of the window 146. In anotherembodiment, the base 142 has a more solid platen configuration, and thewindow 146 is formed into the platen configuration. To provide aclearance between the sharpened edge 136 of the die 122 and the tissue102 to thereby prevent damage to the tissue 102, the base 142 has athickness that is greater than the height of the exposed portion 129(FIG. 3 ) of the die pattern 126.

The handle 144 extends from the base 142 and is configured to provide agrip. Although the handle 144 is illustrated as being substantiallyrectangular in configuration, other shapes may alternatively beemployed. Additionally, although the handle 144 is illustrated asextending substantially perpendicular relative to the base 142 in FIG. 4, it will be appreciated that the handle 144 can extend at another anglerelative to the base 142. For example, the handle 144 can be disposed onthe same plane as the base 142 and may not be angled relative to thebase 142. In another example, the handle 144 is disposed at a 45 degreeangle relative to the base 142. In other embodiments, other placementangles may be more conducive.

The shield 124 thus elevates the sharpened edge 136 of the die 122 abovethe tissue 102 on the platform 112. The bifurcated prongs 148 are usefulfor supporting the plate 125 to the outside of the exposed portion 129of the die pattern 126, which avoids blocking the opening 128 oropenings. Further, the thin prongs 148 reside outside of the die pattern126, and thus outside of the subsequently cut leaflet, thus preventingdamage to the leaflet by the weight of the prongs. Of course, otherarrangements for elevating the sharpened edge 136 above the tissue 102are contemplated, including mounting the die 122 on a mechanism capableof vertical movement such that the die can be independently elevated andthen lowered to cut the leaflet. One such mechanism is described below.

FIG. 5 is a flow diagram of a method 500 of processing pericardialtissue. The method 500 includes positioning a die-cut assembly thatincludes a shield and a thickness gauge over the pericardial tissue,block 502. The die-cut assembly can be configured similar to die-cutassembly 106 of FIG. 1 and includes a die having a plate, a die pattern,and an opening. The die pattern is attached to the plate, and theopening is formed in the plate to provide access to the pericardialtissue which is positioned to lie flat on surface below the die-cutassembly. Next, a thickness of the tissue is measured through theopening, block 504. Thickness is measured by a thickness gauge, such asthickness gauge 104 of FIG. 1 . The thickness gauge can include ameasurement probe that can perform a single measurement at a time, in anembodiment. In another embodiment, the thickness gauge may have ameasurement probe that obtains multiple measurements at severallocations simultaneously. Or as described below, a plurality ofmeasurement probes can perform the measurements simultaneously orsequentially.

In an embodiment, the plate includes more than one opening, for example,three openings, and block 504 is performed by measuring the thickness ofthe tissue through the three openings. As alluded to briefly, in anotherembodiment, the measurements through the three openings can be performedsubstantially concurrently by employing a suitably configured thicknessgauge. As described in detail above, the shield prevents damage to thetissue from the sharp cutting edge of the die during the measurement ofthe tissue thickness by elevating the cutting edge above the tissueuntil it is time to cut the leaflet. At block 506, a section of thepericardial tissue from which a leaflet will be formed is selected,based in part on the thickness measurement of the tissue. Then, theshield is removed and the selected section of the pericardial tissue iscut with the die, block 508, to form the leaflet. The leaflet is thensent on for further processing.

By providing the above-described system 100 and method 500,manufacturing prosthetic valve components, such as leaflets, is bothsimplified and optimized. Additionally, measuring the thickness of aselected portion of the tissue immediately prior to cutting, and withoutthe need to position or reposition the die prior to cutting, reduces alikelihood of misidentification of an area of the tissue to be cut.Moreover, by using the aforementioned techniques, formation of theprosthetic valve components is less laborious and less time-consuming.

FIG. 6 illustrates an exemplary prosthetic heart valve leaflet 200formed in accordance with the principles of the present application. Asmentioned above, the leaflet 200 typically includes an arcuate cusp edge202 opposite a free or coapting edge 204. A pair of side tabs 206extends in opposite directions on either side of the coapting edge 204,and in between the coapting edge and the cusp edge 202. The coaptingedge 204 may be straight, or may be shaped such as shown to have aslight trapezoidal extension 208 in the middle to facilitate coaptationwith the other leaflets. The peripheral edges, including the cusp edge202, coapting edge 204, and side tabs 206, circumscribe a central region210. The leaflet 200 is desirably symmetric about a vertical center lineC/L. When assembled in a heart valve, three identical leaflets 200attach along their cusp edges 202 to a surrounding stent structure, witheach side tab 206 being attached to the stent structure and to a sidetab of an adjacent leaflet. The three coapting edges 202 meet or coaptin the flowstream of the implanted valve to close off backflow indiastole, and are then forced open in systole. The stresses on theleaflets from the oscillating fluid flow are greatest toward the edgeswhere the leaflets attach (typically with sutures) to the stentstructure (or fabric coverings thereof). Indeed, the tabs 206 arepreferably wrapped around a portion of the stent structure and securedthereto for added strength.

The desired thickness of bovine pericardium for heart valve leafletsvaries with the size of the leaflets, with smaller leaflets generallybeing thinner than larger leaflets. Preferably, a majority of eachleaflet is a single desired thickness. Typically, harvested bovinepericardial tissue ranges in thickness from 250 microns up to 700microns, though most of the material is between 300-700 microns thick.Heart valves with extended durability have had bovine pericardialleaflet thicknesses ranging from 0.009-0.023 inches (˜230-580 microns),with smaller valves utilizing thinner leaflets and larger valves havingthicker leaflets.

FIGS. 7 and 8 are magnified perspective and sectional views of twosamples of fixed bovine pericardial tissue. These views illustrate thesomewhat uneven cross-sectional composition of the tissue, as well as aporous or generally heterogenous structure, in particular as seen inFIG. 8 . The present application accommodates the varied physicalstructure of bioprosthetic tissue, in particular bovine pericardium.That is, the measurements are done using a thickness gauge having acontact probe which lightly compresses the tissue for a predeterminedtime period. FIG. 7 shows a sample of fixed bovine pericardium having agenerally uniform thickness, which would be suitable for use in formingleaflets for a bioprosthetic heart valve.

FIGS. 9A-9D illustrate a semi-automated system 300 for assessing andcutting heart valve leaflets from pericardial tissue 302. The tissue 302is shown as an enlarged sheet which can be formed from a pericardialsac, using bovine, equine, porcine, or other such animal sources. Thetissue 302 lies flat on a platen 304 that is desirably movable in two orthree axes underneath a measurement and cutting head 310. An outline ofa heart valve leaflet 306 is shown beneath the measurement and cuttinghead 310, along with the outline of four circles 308 within the leafletoutline. The outlines of the leaflet 306 and circles 308 are shownmerely to illustrate the location of a target area being assessedunderneath the head 310.

The measurement and cutting head 310 includes a plurality of verticaldistance thickness gauges or measurement sensors that end in contactprobes 312 arranged in a particular pattern over the target area of theleaflet outline 306. More specifically, the vertical profile of thesensor probes 312 is indicated by the circles 308 within the leafletoutline. That is, when the sensor probes 312 descend to measure thethickness of the tissue 302, they contact the tissue at the circles 308.In the illustrated embodiment, there are four such sensor probes 312arranged substantially contiguously within the leaflet outline 306.

A preferred arrangement of sensor probes 312 is shown in phantom in theplan view of the leaflet 200 of FIG. 6 . In particular, three sensorprobes 312 contact the tissue substantially in a line, while a fourthsensor 312 contacts the tissue at a location that is perpendicular tothe middle of the three sensors. This abbreviated T-shaped pattern isintended to provide a thickness measurement for a heart valve leafletthat substantially encompasses the central region 210, within theperipheral edges 202, 204, 206. The four sensors 312 thus provide arelatively accurate measurement of an area of tissue large enough fromwhich to cut a heart valve leaflet.

In any event, the number of sensor probes 312 and their pattern canvary. For example, for an even more accurate measurement of thickness,more than four sensors can be utilized to obtain more data points.Alternatively, a single sensor can be used which is moved to the fourlocations shown, though the process takes a bit longer. Furthermore, therelative locations of the sensors can be modified to providemeasurements of particular patterns across an area to be cut into aleaflet. For example, measurements of the thickness along radial linesfrom the center of the coapting edge 204 to the arcuate cusp edge 202can be made to obtain leaflets having uniform thicknesses along theseradial lines. Likewise, measurements of the area corresponding to thecusp edge 202 can be made to ensure that the tissue in the area is nothinner than the central region 210.

The sensor probes 312 are desirably stainless steel with circular feet.The feet are dropped from a small height so as to lightly compress thetissue for a predetermined time period and obtain a measurement of thephysical thickness by compressing any unduly porous portions of thetissue. All four probes can be dropped at once, or they can be actuatedsequentially. Preferably, the compressive force exerted on the tissue byeach probe is the same as the other probes, and a force sensor may beincluded in the platen 304, for example, to ensure uniformity.Alternatively, periodic monitoring may be done, such as measuring theprobe drop force before and/or after a series of thickness measurementsare taken.

With reference back to FIG. 9A, the measurement and cutting head 310further includes an indicator display 320 and a plurality of LED panels324 along the front, the number of which corresponds to the number ofsensors 312. An electronic control and feedback system (not shown) iscalibrated to change the color of the LED panels 324 based on themeasurements taken by the four sensors 312. More particularly, the colorof the respective LED panel 324 desirably changes from off (gray) togreen when the thickness measured by each of the sensors 312 fallswithin a particular range. For instance, for a small bovine pericardialleaflet desirably having a thickness of between 0.009-0.011 inches(˜230-280 microns), each of the LED panels 324 is illuminated with greenLEDs if the respective sensor 312 measures between that thickness range.Alternatively, an actual thickness readout may be provided for eachsensor 312, as well as other equivalent indicators.

The measurements and cutting head 310 further includes a cuttingassembly 330 including a cutting die (schematically shown at 331 in FIG.9C) in the shape of a heart valve leaflet mounted to the undersidethereof. The cutting die may be similar to the die described above foruse in a more manual operation, and typically includes a die patternhaving a lower sharpened edge. The cutting assembly 330 thus correspondsto the die 122 described above, and includes openings through which themeasurement sensor probes 312 pass.

In the sequence of FIGS. 9A-9D, the operator (or computer, if machinecontrolled) locates a predetermined untested patch of tissue 302 beneaththe measurement and cutting head 310. For instance, in FIG. 9A thedashed outline of the leaflet 306 indicates the area to be tested. Thefour LED panels 324 are showing gray, or off, to indicate no measurementhas been taken. Then, as in FIG. 9B, the sensor probes 312 are droppedonto the tissue 302, either simultaneously or one-by-one. The outputs ofeach of the sensor 312 readings shows up on the LED panels 324 as eithera green color for a measurement within the desired range, or a red colorto indicate outside the range. As can be seen, all four LED panels 324are green, signifying that the area of tissue underneath the measurementand cutting head 310 is suitable for that particular thickness ofleaflet. FIG. 9C shows the cutting assembly 330 lowered so that theleaflet cutting die (schematically shown at 331) contacts the tissue 302and cuts the leaflet. Just prior to or during this stage the sensorprobes are lifted back to their original raised positions. Finally, FIG.9D shows the cutting assembly 330 having been raised, revealing a cutleaflet 332. The leaflet can be removed for further processing, or moreareas of the tissue 302 may be assessed and more leaflets cut, ifappropriate. It will be apparent to those of skill in the art thatsetting up a bovine pericardial sac on the platen 304 and programming acontrol system enables the entire sac to be assessed and leaflets cuttherefrom without further operator input.

The measurement sensors may take a variety of forms, but can generallybe categorized as those sensors that contact the bio-material. Contactsensors are designed to produce a signal upon contact with thebio-material that, in combination with knowledge of the relative heightof the sensor above the work surface, determines the thickness of thebio-material. The present invention encompasses any sensor that candetect the thickness of a material relative to a reference surface onwhich the material is placed.

While embodiments and applications of this invention have been shown anddescribed, it would be apparent to those skilled in the art that manymore modifications are possible without departing from the inventiveconcepts herein, and it is to be understood that the words which havebeen used are words of description and not of limitation. Therefore,changes may be made within the appended claims without departing fromthe true scope of the invention.

What is claimed is:
 1. A system for assessing and cutting sheetbioprosthetic tissue, comprising: a flat platen on which a sheet ofbioprosthetic tissue may be supported; a measurement and cutting headmounted above the platen having a vertically-movable die for cuttingbioprosthetic tissue on the platen, the die having a sharp die cuttingpattern defining an opening within an outer boundary, the measurementand cutting head comprising an automated elevation system that can raiseor lower the die to various heights relative to the platen and adistance measurement gauge with a vertically movable probe adapted topass through the opening and measure the thickness of the bioprosthetictissue on the platen; an indicator panel that displays the indication oftissue thickness from the probe; and a die control for lowering the dieand cut bioprosthetic tissue on the platen.
 2. The system of claim 1,wherein the die includes a plate defining a plurality of the openingswithin the outer boundary.
 3. The system of claim 2, wherein thedistance measurement gauge has a plurality of the vertically movableprobes each of which is aligned with one of the openings, and theindicator panel displays the indication of tissue thickness from all ofthe probes.
 4. The system of claim 1, wherein the distance measurementgauge has a plurality of the vertically movable probes which are alignedto pass simultaneously through the opening within the outer boundary,and the indicator panel displays the indication of tissue thickness fromall of the probes.
 5. The system of claim 4, wherein the indicator panelhas a plurality of LED indicators, one for each probe, and the indicatorpanel is calibrated to illuminate each LED with a particular color whenthe associated probe measures the tissue thickness within apredetermined desirable range.
 6. The system of claim 1, wherein thevertically movable probe is weighted and configured to be dropped from apredetermined height so as to compress the bioprosthetic tissue, and thedistance measurement gauge is calibrated to leave the probe in a droppedposition for a predetermined time period prior to measuring thethickness of the tissue with the probe.
 7. The system of claim 6,wherein the vertically movable probe is stainless steel with a circularfoot that contacts the bioprosthetic tissue.
 8. The system of claim 1,further including an automated movement system adapted to displace theplaten horizontally in two axes under the measurement and cutting head.9. The system of claim 8, wherein the automated movement system isadapted to displace the platen in three axes.
 10. The system of claim 1,wherein the die cutting pattern is in the shape of a heart valveleaflet, and there are at least three of the vertically movable probes.11. A system for assessing and cutting sheet bioprosthetic tissue,comprising: a flat platen on which a sheet of bioprosthetic tissue maybe supported; a measurement and cutting head mounted above the platenhaving a vertically-movable die for cutting bioprosthetic tissue on theplaten, the die having a sharp die cutting pattern defining an openingwithin an outer boundary, the measurement and cutting head comprising aplurality of vertically movable probes each adapted to pass through theopening and measure the thickness of the bioprosthetic tissue on theplaten; an indicator panel that displays the indication of tissuethickness from the probes, wherein the indicator panel is calibrated toprovide a positive indication when each probe measures the tissuethickness within a predetermined desirable range; and a die control forlowering the die and cut bioprosthetic tissue on the platen.
 12. Thesystem of claim 11, wherein the die includes a plate defining aplurality of the openings within the outer boundary.
 13. The system ofclaim 12, wherein the each of the vertically movable probes is alignedwith one of the openings.
 14. The system of claim 11, wherein theopening is large enough for all of the vertically movable probes to passsimultaneously therethrough.
 15. The system of claim 11, wherein theindicator panel has a plurality of LED indicators, one for each probe,and the indicator panel is calibrated to illuminate each LED with aparticular color when the associated probe measures the tissue thicknesswithin the predetermined desirable range.
 16. The system of claim 11,wherein the vertically movable probes are weighted and configured to bedropped from a predetermined height so as to compress the bioprosthetictissue, and the distance measurement gauge is calibrated to leave theprobe in a dropped position for a predetermined time period prior tomeasuring the thickness of the tissue with the probe.
 17. The system ofclaim 16, wherein the vertically movable probe is stainless steel with acircular foot that contacts the bioprosthetic tissue.
 18. The system ofclaim 11, further including an automated movement system adapted todisplace the platen horizontally in two axes under the measurement andcutting head.
 19. The system of claim 18, wherein the automated movementsystem is adapted to displace the platen in three axes.
 20. The systemof claim 18, wherein the measurement and cutting head comprises anautomated elevation system that can raise or lower the die to variousheights relative to the platen.
 21. The system of claim 11, wherein thedie cutting pattern is in the shape of a heart valve leaflet, and thereare at least three of the vertically movable probes.